异构环境下多媒体电子邮件用户代理的设计与实现

用户代理的多媒体化是建立多媒体电子邮件系统的关键。本文对文本邮件系统分层模型进行了扩充，提出了在异构环境中以演示模式为基础的邮件转换方法，描述了一个能进行有效时空合成和同步操作的多媒体信息模型。最后，基于上述邮件转换方法和信息模型，我们给出了多媒体用户代理ＴＨ－ＵＡ的详细设计和实现方案。     

XML技术在一个PDA邮件代理中的应用

本文首先分析了PDA在电子邮件方面的不足，然后提出为PDA设计邮件代理并简单介绍该邮件代理，最后重点讲述如何运用XML技术设计与实现代理用户的配置文件，并对系统的未来发展进行展望。     

面向安全检测的SMTP透明代理服务器

通过对SMTP协议和SMTP代理服务器原理的分析，在Linux环境下开发了面向安全检测的SMTP透明代理，设计并实现了一些关键技术，包括端口重定向、并发邮件服务、获取邮件服务器的地址和端口号、处理附件等。测试表明，该系统实现了用户透明功能，可以代理多种邮件服务，有效地防止了病毒入侵和内容泄露。     

基于XML的配置文件技术在邮件代理系统中的应用

简述了邮件代理系统的主要功能和运行流程，重点阐述了XML技术在该系统用户配置文件中的应用。通过分析PDA等移动设备在电子邮件方面的不足，提出了一个邮件代理系统的设计框架及实现流程，给出了配置文件的功能介绍和XML文档结构的树型表示，以及配置文件的定义和具体解析过程。最后详细阐述了如何运用XML技术具体设计与实现用户的配置文件，并对整个系统进行了评价和展望。     

电子邮件UA与MTA间抗抵赖协议的研究与实现

抗抵赖服务旨在生成、收集、维护已声明的事件或动作的证据,并以此证据解决关于某事件发生或未发生而引起的争议 .抗抵赖协议借助密码学算法以实现抗抵赖服务 .提出了一种用户代理与传输代理间的双方不可否认协议NRPUM,并将其封装到邮件传输协议SMTP与POP3中,以实现用户代理与传输代理间的邮件抗抵赖 .经过分析以及实验验证,该抗抵赖方法能够完成用户代理与传输代理间的不可否认性 .     

基于电子邮件方式传输数据的软件模块设计

研究并设计了电子邮件MUA（Mail User Agent，邮件用户代理）软件模块，给出了实现电子邮件数据流处理及通讯协议实现的具体细节。该模块严格遵循RFC文档，融合服务器认证过程，可以接入Internet上规范的邮件服务器；提供丰富的程序接口，可作为应用系统中的一个通讯模块使用。     

基于XML的配置文件技术在PDA邮件代理系统中的实现

本文主要介绍了PDA电子邮件代理系统,重点阐述了XML技术在该系统用户配置文件中的应用。本文通过分析PDA在电子邮件方面现有的不足,首先提出了一个PDA邮件代理系统的设计框架及实现流程,最后详细阐述了如何运用XML技术具体设计与实现用户的配置文件,并对整个系统进行了客观的评价和展望。     

JAVA实现基于LDAP的分布式WebMail系统

文章在讨论轻量级目录访问协议LDAP、Java技术和Qmail邮件服务器的基础上,设计并实现了一个分布式WebMail系统。该系统以Qmail作邮件代理、LDAP存放用户帐号信息、JSP技术编程,具有较好的可移植性、可扩充性和安全性。     

Win95／WinNT环境下电子邮件服务器的设计与实现

本文介绍了Win95，WinNT下基于SMTP／POP3协议的E－Mail服务器的设计与实现。首先介绍了Internet电子邮件的组成部分，用户代理（UA）和报文传输代理（MTA）的概念，以及它们在Internet电子邮件中的作用，给出了典型的SMTP／POP3客户／服务器的组成。其次，简单地介绍了简单邮件传输协议（SMTP）和邮局协议（POP3）的工作原理、特点。接下来，给出了实现的邮局服务器的系统功能、系统框架图和运行流程、以及主要功能的实现原理，详细地介绍了有关的数据结构。最后给出了系统的改进和升级的一些设想。     

基于XML结构的电子邮件的表示及其生成

电子邮件通常按半结构化的MIME格式进行封装和传输，并以各个邮件用户代理专用的数据格式进行存储，无法同其它应用程序共享电子邮件，也无法充分利用电子邮件这一信息源。该文提出了一种面向邮件客户端的电子邮件的XML表示方法，将邮件的XML标记进一步地细化，目的是便于电子邮件的检索和重组，并给出了从邮件的MIME源码到邮件的XML文档的转换方法，为邮件的后续操作和邮件库的充分利用提供基础。     

System Architectural Design for DeliveringVideo Mail over the World-Wide-Web

This paper examines the feasibility of providing multimedia mail,in particular video mail,on the existing World-Wide-Web platform.In this instance, the Web browser will act as the user agent of the mailing system.With this,users will be able to compose,send and read video mail directly on the Web, This paper examines a number of different system architectures which can be employed for the development of Video Mail.Based on the following key issues:portability of system,flexibility of system,Internet standard support,security and authentication,and message compression and storage,a final architecture was chosen to build Video Mail.The approach taken is that the system will be interfaced to the Web using a standard Hyper Text Transfer Protocol(HTTP) server and a standard Web brower.This is achieved through the use of Common Gateway Interface(CGI) programs and forms which reside in a standard HTTP server to provide the functionality of video mail,and a separaete mail server for the storage and management of messages.This will cause the HTTp server to behave as if it is an electronic mail system.The paper also addresses implementation issues pertaining to the use of CGI programs,mail server development,and video and auidio composition and playback.     

Delivery of video mail on the World Wide Web

This study was initiated to examine the feasibility of providing multimedia mail, in particular video mail, on the existing World Wide Web platform. In this instance, the Web browser will act as the user agent of the mailing system. With this, users will be able to compose, send and read video mail directly on the Web. This paper examines a number of possible system architectures that can be employed for the development of video mail. Based on the following key issues: portability of system, flexibility of system, Internet standard support, security and authentication, and message compression and storage, a final architecture was selected to build video mail. The approach taken is that the system will be interfaced to the Web using a standard HyperText Transfer Protocol (HTTP) server and a standard Web browser. This is achieved through the use of Common Gateway Interface (CGI) programs and forms which reside in a standard HTTP server to provide the functionality of video mail, and a separate mail server for the storage and management of messages. This will cause the HTTP server to behave as if it is an electronic mail (E-mail) system. Video mail has been successfully implemented at the School of Applied Science, Nanyang Technological University, Singapore. The development work has been carried out on a Sun SPARC5 workstation and the Typhoon relational database system was used to construct the mail server. All software codes were written in C or C++. A video capturing application used in conjunction with a SunVideo card has been developed for video and audio recording. The paper also addresses implementation issues pertaining to the use of CGI programs, mail server development, and video and audio management.     

多媒体对象的Agent展示集成模型*

根据多媒体对象的面向对象特点,给出了一种基于“事件-条件-动作”的Agent展示集成模型.该模型集对象的内容、时序、空间关系于一体,通过消息传递与对象展示状态事件控制对象展示集成的行为,保证了对象的封装性,并对用户的交互提供有力的支持,是一种动态集成模型.“事件-条件-动作”机制是主动数据库中广泛采用的方法,已有成熟的技术支持.通过对Allen所定义的时序关系的表示,说明了模型的表达能力,并通过实例加以验证.指出了展示集成模型在多媒体数据库中的作用.     

利用电子钱包的公正支付系统

提出了一种利用电子钱包的公正支付系统,用户在银行有一个和身份相联系的个人帐号,在所持的电子鲆包中有一个和身份没有联系的匿名帐号。用户在银行提款时,将钱从他的个人帐号转到电子钱包中的匿名帐号,而不泄露个人帐号和匿名帐号的联系,以后用匿名帐号支付。     

利用电子钱包的有效的公正支付系统

该文提出了一个有效的利用电子钱包的公正支付系统。系统中用户只拥有一个银行账号;提款时用户得到一个关于本人身份字的盲签名并向银行提供构造正确的供跟踪的信息;支付时用户在防窜扰卡的协助下向商家证明所支付电子现金的有效性,并提供可跟踪的正确信息;委托人完全离线,不参与系统中除跟踪协议以外的任何协议的执行,仅需要保存好自己的密钥并在需要跟踪时使用之。系统的安全性基于离散对数困难问题,分析表明该系统是安全有效的。     

Managing copyright in open networks

The need for an electronic copyright management system (ECMS) that protects intellectual property rights (IPR) in open network environments continues to grow. Network security issues are classically handled through cryptography; however, cryptography ensures confidentiality, authenticity, and integrity only when a message is transmitted through a public channel, such as an open network. It does not protect against unauthorized copying after the message has been successfully transmitted. Digital watermarking is an effective way to protect copyright of multimedia data even after its transmission. A watermark, embedded in the data, can uniquely identify the document's owner or authorized user. The main problem with using watermark technology, for IPR protection, however, is its reversibility. Anyone who can read or detect the watermark can also remove it by inverting the watermark process. Our open network ECMS combines watermarking with cryptography to achieve reliable copyright protection while satisfying two contrasting requirements: actors in ECMS transactions must be able to verify that the watermark granting their rights is truly embedded in the multimedia document; and actors (other than the author) must not be able to remove the watermark     

SIP UA与STUN CLIENT互通的新方案

针对SIP用户代理和STUN客户端互通方案的不足,提出了一种新的互通方案.该方案设计了一个SIP用户代理和STUN客户端都可以访问的配置文件作为接口文件,从而使二者成为相互独立的实体.SIP用户代理不需要嵌入STUN客户端,也无需改造其整体架构,仅需读取接口文件的配置信息来完成其系统的初使化,并以文件读取的方式实现SI...     

Collision Attacks With Budget Constraints on Key Management Schemes for Secure Multimedia Multicast

We address the problem of distributing a confidentially shared session key to a multimedia multicast group for content protection. In two such schemes proposed by Trappe , the session key is distributed by employing a homogenized rekey message format. We show that their rekey algorithm in itself is vulnerable to specialized collision attacks, in which even a completely passive outer adversary, who never joins the system and thus never knows any secret user keys, can still reveal the session key of the multimedia multicast with an observable probability but only involving a time complexity far lower than an exhaustive search.      

异地计算机教学与训练系统的结构模型研究

异地计算机教学与训练系统就是利用计算机网络环境，向分布在异地的授课者和学习者提供一种模拟面对面教学和训练的虚拟环境。